Two-step roller finger followers (RFF) for the controllable lift of compression valves in a valve train of an internal combustion engines are well known. An RFF extends between a hydraulic lash adjuster (HLA) and the stem of a valve. Engagement with an eccentric cam lobe of an engine camshaft causes the RFF to be pivoted about the HLA and thereby to depress the valve stem, opening the valve. A two-step RFF mechanism allows an engine valve to be operated by two different cam lobe profiles, one with the mechanism locked, providing a high valve lift, and the other with the mechanism unlocked, providing a lower lift or no lift.
When the mechanism is unlocked, the RFF portion that is not directly in contact with the valve stem and the HLA, known in the art as the high-lift follower, typically is provided with a biasing spring, known in the art as a “lost-motion” spring, to keep that portion in contact with the cam. A lost-motion spring, which may be a torsional spring or a compression spring, is disposed in compression between the high-lift follower and the remainder of the RFF, known in the art as the body or low-lift follower, which is directly in contact with the valve stem and the HLA. Thus, when the high-lift follower engages the cam lobe, a force is exerted by the spring against the HLA. If the force of the lost motion spring is too small, the high-lift follower may not be able to stay in contact with the high-lift cam lobe under all engine operating conditions causing valve train clatter. If the spring force is too large, the force of the lost motion spring may overcome the force of an internal spring in the HLA, causing the HLA to leak down and become undesirably compressed and depleted of oil.
In cases where the lost motion spring exerts a greater force than the internal spring in the HLA, excessive leak-down can be prevented by mechanically limiting the amount of relative travel between the high-lift follower and low-lift follower, as imposed by the lost motion spring, when the high-lift follower is in contact with the base circle of the high-lift cam. This can be done by providing a mechanical stop that limits the rotation of the high-lift follower relative to the low-lift follower hereafter referred to as the z-stop.
Also, in a two-step RFF having a spool-type roller set wherein the roller shaft of the set contains a roller at each end and extends through the RFF, roller bearing assemblies are disposed in opposing walls of the low-lift follower to support rotation of the roller shaft. The bearings are self-contained in the assembly. That is, the assembly includes a cup-shaped housing for receiving the bearings, the housing being closed at each lateral end to restrain the bearings laterally. Because of the need to roll-over or close the ends of the assembly to retain the roller bearings therewithin, at least one end of the housing must be non-hardened, and the bearings shortened to fit within the shortened housing. Shorter bearings reduce the life and durability of the bearings and can cause excessive wear to the mating components served by the bearings. Further, a non-hardened housing as required for rolling over the end of the housing cannot be also employed as a satisfactory z-stop for the high-lift follower.
What is needed in the art is a two-step roller finger follower having an improved z-stop arrangement wherein unacceptable HLA leak-down, caused by the compressive force of the lost motion spring, is prevented.
What is also needed in the art is an improved roller shaft bearing for increased bearing life.
What is further needed in the art is an improved roller shaft bearing arrangement that also provides a z-stop arrangement.
It is a principal object of the present invention to prevent unacceptable HLA leak-down caused by compressive force of the lost motion spring.
It is a further object of the invention to increase roller shaft bearing life through the use of longer bearings.
It is a still further object of the invention to provide both an improved bearing and a z-travel stop feature in a roller shaft bearing arrangement.